Instrument scale length multiplier



Nov. 15,1938. B. H. SMITH 7,

INSTRUMENT SCALE LENGTH MULTIPLIER' Filed June 26, 1936 WITNESSES: v INVENTOR W/M fle/jazW h A, 5277/7/7.

ATTO Y Patented Nov. 15, 1938 I 137,066.

UNITED STATES PATENT or-rice INSTRUMENT scam LENGTH MUumgm-m Benjamin H. Smith, Bloomfield, N. 1., asslgnor.

which are now in general use are capable of a Quite obviously, with this type of construction, 5 scale length indication of 90 or less. This is by an indication of more than 90"v is not desirable, reason of the fact that the shaft of the coil or and quite obviously, the torque developed is quite vane, to which the indicating hand is secured, is low. capable of only about a 90 rotation. A segmental gear I2 is rigidly secured to the The desire has been frequently expressed for an shaft 4 for rotation therewith and drives a pinion 10 instrument of this type having a.substantially l4 secured to a spindle l6 rotatablysupported greater scale length to increase the accuracy of as by a bracket l8 depending from the permanent readings and to facilitate making such readings. agnet. The gearing arrangement is such that,

- Accordingly, it is an object of the present inwith the construction shown, a 90 rotation of the i5 vention to provide an indicating instrument, of shaft 4 will move the spindle l6 and the pointer is the moving-coil or repulsion-vane type with a secured thereto through appr tely 270. pointer movable over a scale which may be as A second spiral spring 22 has one end thereof much as 360, if desired. This is accomplished, c ed to the bracket l8 and the other to the in accordance with the invention, by providing spindle IS in such manner that it tends to bias 20 gearing betwee the shaft of the instrument the pointer 20 to the zero position on the scale, 20 movement and'the spindle upon which the indias shown. A stop 24 may be provided at the zero catingpointer is mounted which magnifies the DQ o or insurifigthat the pointer oes not movement of the latter with respect to the go below such point. I f rm r. Althoughv the spiral spring I0 is inherently 25 It is known that gearing between meter movevery weak because the torque which it opposes is 25 ments and their indicating pointers is broadly Very small, the spiral spring 22 is preferably of old. However, in such cases theinstrument is of the lowest strength obta and Substantially a type which develops asubstantial torque, makl ss than that of the spring Ill. The prin ing t problem simple wit t eleefunction of the spring 22 is to prevent backlash 0 trical indicating instrument of the moving-coil or between the gears and W The gearing, Of 0 repulsion-vane type, however, the power deand particularly the segmental gear veloped in the movement is very small and the is of very light construction to minimize the load addition of gearing of any kind has been eo imposed on the shaft 4,-and to minimize friction.- sidered prohibitive. In the construction herein- The Spring 22 p s. to a Slight degree, e

after described, the effect of friction in thegearo que of shaft 4. but introduces no error in the 35 ing and the undesirable backlash in such gearing instrument f d because the instrument is has been eliminated or reduced to a point where calibrated with t springs in op ation. the instrument movement torque can accurately i accordance with the construction s d, drive t indicating i t an instrument having a scale much longer than 40 Referring to the accompanying drawing: these et fore used is possible without sacrific- 40 Figure 1 is a view in front elevation of an indimg the accuracy of the indication which would eating instrument movement with a portion of usually be caused y friction in the gearing 01 the face broken away to disclose the details of other additional load 0n he movement of the the present invention; and armatulie h Fig. 2 is a .view partly in section and partly in Quite obviously, the construction disclosed is 45 side elevation of the instrument movement shown equally app le to her type e q e in Fig instruments in which the armature is capable of For purposes of illustration, t indicating only a limited movement. Also, modifications in t t movement Shown and described is of the construction illustrated may be resorted to the dArsonval or moving-coil type having a mov- Without departing rom the spirit of the inven- 50 b 11 2 fixed t men 4 journeled-in suitable tion, and it is intended that no limitations shall hearings or arbors 6 mounted across the poles of he placed p the invention except as p sed a permanent magnet 8. As is well understood, by h Prior t and ppe ed claims. energization of the coil2 causes a reaction with I claim as my invention:

the field of the permanen magnet 8 t rotate the 1. An electrical indicating instrument having 55 to Westinghouse Electric Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 26, 1936, Serial No. 87,371. 3 Claims. (Cl. 1712-) The invention relates to electrical measuring instruments and particularly to instruments of the dArsonval, repulsion-vane and similar types.

Indicating instruments of this general type coil and its shaft 4. In this type of instrument, the movement of the shaft 4 is restrained by a carefully calibrated spiral spring H) which tends to rotate the shaft 4 ,toward a zero position.

a rotatable armature capable of rotation through 90 or less, and a. spiral spring for biasing it to a zero position, an indicating pointer and a spindle for rotatably mounting it for movement over a scale substantially greater than 90, means constituting a driving connection between said armature and spindle to move the pointer substantially completely over said scale, and a second spiral spring for biasing said pointer toward a zero position orr said scale, said second spring being substantially weaker than the first mentioned spring.

2. An electrical indicating instrument including a shaft and means for rotating it in response to an electrical quantity to be measured, an indicating pointer and a spindle for rotatably mounting it for movement with respect to an arcuate scale, gearing constituting a driving connection between said shaft and spindle comprising a segmental gear secured to said shaft for cooperation with a gear secured to said spindle, a restraining spring operating on said shaft to bias it against the force exerted by the measured quantity, and

a spring for biasing said spindle to its zero position with respect to said scale, the spring on said spindle being substantially weaker than that on said shaft and being of just sufiicient strength to maintain driving connection between said ears to avoid backlash therebetween.

3. An electrical indicating instrument including a shaft and means for rotating it in response to an electrical quantity to be measured, an indicating pointer and a spindle for rotatably mounting it for movement with respect to an arcuate scale, gearing constituting a driving connection between said shaft and spindle, a calibrated restraining spring for said shaft for biasing it against the force exerted by the measured quantity, and a second spring mounted to bias said spindle against rotation by said driving connection, said second spring being only of sufiicient strength to maintain continuous contact between the gearing of the driving connection to prevent backlash therein.

BENJAMIN H. SMITH. 

